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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] huge tcp performance-regression on pvops - kernel (+Solution)
On Tue, Oct 27, 2009 at 12:37:25AM +0100, Ronny.Hegewald@xxxxxxxxx wrote: > < xmlns="http://www.w3.org/1999/x"; xml:lang="en" > lang="en"><title></title><head><meta http-equiv="Content-type" > content="text/; charset=UTF-8" /><style type="text/css"> , body {overflow-x: > visible; } { width:100%; height:100%;margin:0px; padding:0px; overflow-y: > auto; overflow-x: auto; }body { font-size: 100.01%; font-family : Verdana, > Geneva, Arial, Helvetica, sans-serif; background-color:transparent; > overflow:show; background-image:none; margin:0px; padding:5px; }p { > margin:0px; padding:0px; } body { font-size: 12px; font-family : Verdana, > Geneva, Arial, Helvetica, sans-serif; } p { margin: 0; padding: 0; } > blockquote { padding-left: 5px; margin-left: 5px; margin-bottom: 0px; > margin-top: 0px; } blockquote.quote { border-left: 1px solid #CCC; > padding-left: 5px; margin-left: 5px; } .misspelled { background: transparent > url(//webmailerng.1und1.de/static_resource/mailclient/widgets/basic/parts/maileditor/spellchecking_underline.gif) > repeat-x scroll center bottom; } .correct {} .unknown {} .ignored > {}</style></head><body id="bodyElement" style=""> > <p>Setup: pvops dom0 kernel 2.6.31.4 from Jeremys git-repository from > 2009-10-18<span></span></p><p id="__paragraph__1256597098000" style=""><span > style=""><br></span></p>Problem: Very slow network-performance (3-10 kbs) > when tcp-packets are used (noticed when using scp, samba, nfs over tcp)<p > id="__paragraph__1256597073000" style=""><br></p><p > id="__paragraph__1256597073000" style="">But this occurs only in the > following situations:<br></p><p id="__paragraph__1256597073000" > style=""> <span></span></p><p > id="__paragraph__1256597073000" style="">1.) domU to domU on same PC (domUs > are paravirtualized linux-kernels)<br></p><p id="__paragraph__1256597073000" > style="">2.) domU to another PC that doesn't use<span id="misspelled-have" > class="misspelled" name="misspelled-have"></span> pvops-kernel (packets sent > from another PC to domU works fine)<br></p><br>domU to dom0 and the opposite > way works without performance-regression.<br><br><p>Reason: bigger > tcp-packets get dropped from the domU the tcp-packets are sent from (netstat > -s in domU shows many retransmitted tcp-segments)</p><p><br></p><p>tcpdump > shows that the bigger packets leave the vif from the domU they were sent > from, but never arrive the vif from the domU they are sent > to.<br><span></span></p><br><span style=""></span><p>This is caused by this > lines in drivers/xen/netback.c at line 1325 :<span></span></p><p > id="__paragraph__1256597423000" style=""><br><span style=""></span></p><p > id="__paragraph__1256597423000" > style=""> > if (skb->data_len < skb_shinfo(skb)->gso_size) { > </p><div > class="pre"> > skb_shinfo(skb)->gso_size = 0;</div> > <div > class="pre"> > skb_shinfo(skb)->gso_type = 0;</div> > <div > class="pre"> > }</div><br><p id="__paragraph__1256597121000" style="">These lines were > reverted from the linux-2.6.18-xen mercurial repository <br></p><p > id="__paragraph__1256597121000" style=""><br></p><p > id="__paragraph__1256597121000" style="">on 2009-01-13 in changeset 774: > <a > href="http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/107e10e0e07c";>107e10e0e07c: > netfront/back: do not mark packets of length < MSS as GSO</a></p><p > id="__paragraph__1256598462000" style=""><br><span style=""></span></p><p > id="__paragraph__1256598462000" style=""><span style="">I used the patch on > the above mentioned pvops tree and the problem was > gone.</span><span></span></p><p id="__paragraph__1256600217000" > style=""><br><span style=""></span></p><p id="__paragraph__1256600217000" > style=""><span style="">I never noticed such problems on the 2.6.18-xen > kernel or the forward-ported xen-kernel 2.6.31.4 (from </span>Andrew > Lyon)</p></body></> > Kudos for discovering this. Did you verify whether the domU has the corresponding patch: diff -r 28acedb66302 -r 107e10e0e07c drivers/xen/netfront/netfront.c --- a/drivers/xen/netfront/netfront.c Wed Jan 07 12:21:54 2009 +0900 +++ b/drivers/xen/netfront/netfront.c Tue Jan 13 15:17:54 2009 +0000 @@ -1439,6 +1439,14 @@ np->stats.rx_packets++; np->stats.rx_bytes += skb->len; +#if HAVE_TSO + if (skb->data_len < skb_shinfo(skb)->gso_size) { + skb_shinfo(skb)->gso_size = 0; +#if HAVE_GSO + skb_shinfo(skb)->gso_type = 0; +#endif + } +#endif __skb_queue_tail(&rxq, skb); np->rx.rsp_cons = ++i; Looking at the PV_OPs kernel it doesn't look to be there, but I was wondering if the domU you are using has it? Ian, Would it make sense to remove this changeset if most of the DomU's don't have this fix? _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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